In communication systems, whether they conform to GSM, CDMA, or other technology standards, the communications between the base stations and the mobile terminals typically include one or more traffic channels for communicate traffic data and one or more control channels for exchanging control information or control signals. For some control channels, for example, a pilot channel of CDMA systems, the control information has to be broadcasted omni-directionally to cover the whole or sectored cell. On the other hand, it is desirable to steer narrow beam formed for communicating through traffic channels with specified mobile equipments without interfering others nearby. The beam formed pattern for the traffic data is directed to particular users, and it has a narrow beam width.
The narrow beam width beamforming provides a roughly 9 db performance advantage for the traffic data over control data, as traffic data can be aimed at specific user(s), but control data must be sent to everyone under the coverage of the telecommunication system.
WiMAX is a standards-based wireless technology that provides high-throughput broadband connections over long distances. WiMAX can be used for a number of applications, including “last mile” broadband connections, hotspots and cellular backhaul, and high-speed enterprise connectivity for business.
WiMAX has a special mode to improve control channel efficiency called Diversity Map Scan. This mode is intended to balance the link budget of the control channel for systems using beamforming for traffic data. Unfortunately, without an appropriate scheme, the benefits of beamforming are reduced by high overhead and un-realized range.
When in the Diversity Map Scan mode, the communications system operates by transmitting multiple narrowband signals (called AAS-DLFPs) one after the other in the time domain. FIG. 1 illustrates a frame 100 containing an AAS Diversity Map Zone 102 therein. It illustrates a four-antenna configuration where the AAS preamble and AAS DL MAPs structure are repeated four times to support the corresponding four groups of users. The downlink (DL) subframe includes a non-AAS section and an AAS section specified by information elements provided in a DL MAP. Within the AAS zone, subchannel numbers 4 and N−4 (N is the index for the last logical subchannel) are allocated to the AAS DL MAP where AAS MAP allocations are specified for AAS users.
Within the AAS zone, the AAS BS specifies allocations to be used for Subscriber Station (SS) Ranging. In Time Division Duplex mode, a base station (BS) of the communications system can extract the channel information required for beamforming from Ranging Request messages received from the SS's. In Frequency Division Duplex mode, beamforming is done through AAS Feedback Request and Response messages where channel response information along with information regarding Received Signal Strength Indicator (RSSI) and Carrier to Interference plus Noise Ratio (CINR) are reported back to the BS by the SS.
Each SS must listen to the first preamble of the frame, then looks in a defined zone for additional preambles which indicate the location of these AAS-DLFPs, which must be independently decoded by the SS. After up to 16 AA-DLFPs have been analyzed, the SS picks the best one and reports to the BS which AAS-DLFP had the best signal. The AAS-DLFP then points to a private map with the control information. From this point forward, the BS transmits the control information on the private map until channel conditions force a change.
What is needed is an improved method and system for effectively enhance the communication for the control information between the base station and the subscriber station using beamforming in a wireless communications system.